Scanning probe devices, such as the atomic force microscope (AFM) have proven to be excellent tools for imaging a wide range of materials, such as metals, semiconductors, minerals, polymers, and biomaterials. In an AFM, forces are measured by means of a cantilever that deflects when forces act on it. The deflection of the cantilever is sensed by a detection system, commonly by focusing an incident beam as a spot onto the cantilever and directing the reflected beam onto a segmented detector. Specialized AFMs called “force pullers” have been built for the purpose of pulling on molecules to determine the structure and dynamics of those molecules. AFM-like cantilevers and cantilever arrays have also been used recently as chemical sensing devices. In this mode of operation, a chemically sensitive layer is applied to one of more surfaces of the cantilever. When a target molecule is detected, the cantilever's nanomechanical properties are affected—i.e., the deflection and/or resonant frequency of the cantilever will change.
Since its introduction, the AFM and cantilever sensing devices have become increasingly more advanced, measuring decreasingly smaller forces and utilizing decreasingly smaller cantilevers. This has introduced problems relating to the sensitivity of the instrument. There is a need to provide greater sensitivity and a smaller spot size to accommodate the smaller cantilevers and smaller forces that scientific investigators need to either measure samples or manipulate them. Similar detection techniques are also used to monitor the motion of the optical probes used in Near-Field Scanning Optical Microscopes (NSOM), the scanning ion-conductance microscope (SICM), and a variety of other scanning probe microscopes. The growing field of nanotechnology also provides ample motivation for the precision measurement of the position and/or motion of a wide variety of objects down to the nanometer scale and below.
The following U.S. patents are relevant to this invention: U.S. Pat. No. 5,825,020—Atomic force microscope for generating a small incident beam spot, U.S. Pat. No. RE034489—Atomic force microscope with optional replaceable fluid cell, and U.S. Pat. No. 4,800,274—High resolution atomic force microscope. The following publications are relevant to this invention: (1) Mario B. Viani, et al., “Small cantilevers for force spectroscopy of single molecules;” Journal of Applied Physics, Volume 86, Number 4, pp. 2258-2262. (2) Tilman E. Schaffer, et al., “Characterization and optimization of the detection sensitivity of an atomic force microscope for small cantilevers;” Journal of Applied Physics, Volume 84, Number 9, pp. 4661-4666. (3) Tilman E. Schaffer, et al., “An atomic force microscope for small cantilevers;” SPIE—The International Society for Optical Engineering, Volume 3009, pp. 48-52. (4) D. A. Walters, et at., “Short cantilevers for atomic force microscopy;” Review of Scientific Instrumentation, Volume 67, Number 10, pp. 3583-3590. (5) T. E. Schaffer, et al, “Studies of vibrating atomic force microscope cantilevers in liquid;” Journal of Applied Physics, Volume 80, Number 7, pp. 3622-3627. (6) Deron A. Walters, et al, “Atomic force microscopy using small cantilevers;” SPIE—The International Society for Optical Engineering, Volume 3009, pp. 43-47. The foregoing patents and publications are all incorporated herein by reference.